DHT-Based OFDM Transmitter and Receiver

ABSTRACT

A DHT-based OFDM transmitter and receiver use discrete Hartley transform to implement multicarrier transmission. A transmission terminal (or a receiving terminal) of a transmitter and receiver comprises two IDHT (or DHT) processors and a diagonal processing device. The two IDHT processors make the DHT-OFDM system transmit the 2D modulation signal to increase the bandwidth efficiency. The diagonal processing device is used to diagonalize the circulant channel matrix into discrete memoryless subchannels, and thus only one-tap frequency domain equalizer can compensate the channel effects. Besides, the proposed DHT-OFDM transmitter and receiver are also compatible with a conventional DFT-OFDM system, and they can flexibly works with the conventional DFT-OFDM transmitter and receiver.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a transmitter and receiver and particularly toa DHT-based OFDM transmitter and receiver.

2. Description of the Related Art

The related characteristics of DHT matrix are summarized and then usedto describe the technical problem that the conventional DHT-OFDM systemconfronts.

Characteristics of the DHT Matrix

Firstly, the N×N matrices of DFT and DHT (or IDHT) may be expressed as:

$\begin{matrix}{F = {{\frac{1}{\sqrt{N}}\left( {C + {j\; S}} \right)\mspace{14mu} {and}\mspace{14mu} H} = {\frac{1}{\sqrt{N}}\left( {C + S} \right)}}} & (1)\end{matrix}$

C(l,m)=cos(2πlm/N) and S(l,m)=sin(2πlm/N) are a sin matrix and a cosinematrix, respectively. From the symmetric characteristics of thetrigonometric functions, J_(N)S=SJ_(N)=−S and J_(N)C=CJ_(N)=C can beobtained, in which J_(N) is a N×N permutation matrix and defined asfollows:

$J_{N} = \begin{bmatrix}1 & 0 & \Lambda & \Lambda & 0 \\0 & \; & \; & N & 1 \\M & \; & N & N & {\; 0} \\M & N & N & N & M \\0 & 1 & 0 & \Lambda & 0\end{bmatrix}$

According to the characteristic of real-valued circulant matrix Ã thatcan be diagonalized by the DFT matrix F, an equation is obtained asfollows:

$\begin{matrix}{\Lambda = {{F^{H}\overset{\sim}{A}F} = {{{\frac{1}{N}\left( {{S\overset{\sim}{A}S} + {C\overset{\sim}{A}C}} \right)} + {j\left( {{C\overset{\sim}{A}S} - {S\overset{\sim}{A}C}} \right)}} = {{diag}\left\{ \overset{\rho}{\lambda} \right\}}}}} & (2)\end{matrix}$

To determine whether the circulant matrix is similarly diagonalized bythe DHT matrix, the DFT matrix in equation (2) is replaced with the DHTmatrix H to obtain the result as follows:

$\begin{matrix}{{H\overset{\sim}{A}H} = {{\frac{1}{N}\left( {C + S} \right){\overset{\sim}{A}\left( {C + S} \right)}} = {\frac{1}{N}\left( {{S\overset{\sim}{A}S} + {C\overset{\sim}{A}C} + {C\overset{\sim}{A}S} + {S\overset{\sim}{A}C}} \right)}}} & (3)\end{matrix}$

By applying the trigonometric properties to equation (3),CÃS+SÃC=J_(N)(CÃS+SÃC) is obtained. Thus, by using the result obtainedfrom equation (2), equation (3) can be re-expressed as:

$\begin{matrix}\begin{matrix}{{H\overset{\sim}{A}H} = {{\left\{ \Lambda \right\}} + {J_{N}\left\{ \Lambda \right\}}}} \\{= \begin{bmatrix}{\left\{ \lambda_{0} \right\}} & 0 & \Lambda & \Lambda & 0 \\0 & {\left\{ \lambda_{1} \right\}} & \; & \; & {\left\{ \lambda_{N - 1} \right\}} \\M & \; & O & N & \; \\M & \; & N & O & \; \\0 & {\left\{ \lambda_{1} \right\}} & \; & \; & {\left\{ \lambda_{N - 1} \right\}}\end{bmatrix}}\end{matrix} & (4)\end{matrix}$

Equation (4) apparently shows that the entries ℑ{λ₁, λ₂, . . . ,λ_(N-1)} exist on the anti-diagonal of the HAH matrix, which indicatesthat the DHT matrix cannot diagonalize the circulant matrix.

Conventional 1D DHT-OFDM System

Refer to FIG. 5, a block diagram of a conventional one dimensional (1D)DHT-OFDM system is illustrated (digested from Reference 1, hereafter“R1”). Firstly, the bit stream is transmitted from a transmissionterminal to a PAM mapper 50 to become transmitted data symbol. The datasymbol in R1 must be a 1D constellation point, such as BPSK or PAMsignaling. Each data symbol {d_(k)} should be allocated on twomirror-symmetric subcarriers before feeding into the IDHT processor 70.The IDHT processor 70 is an inverse discrete Hartley transform tomodulate the PAM symbol {d_(k)} to the N orthogonal subcarriers. At thereceiver, the received signal vector

processed by the DHT processor 71 are fed into the one-tap frequencydomain equalizer (FEQ) 72 to compensate the channel effects. The DHTprocessor 71 is a discrete Hartley transform to demodulate each datasymbol {d_(k)} from the N orthogonal subcarriers. Actually, although DHTis different from IDHT in name, they are the same in the definition ofmathematics and are denoted by matrix H. Since half of the data symbolson the mirror-symmetric subcarriers are redundant, they should bedropped before a PAM demapper.

The DHT-OFDM system proposed in R1 is not bandwidth-efficient becauseonly 1D constellation symbol is employed. Therefore, another reference,(hereafter “R2”) proposed a 2D DHT-based OFDM system, of which a blockdiagram is shown in FIG. 6. To transmit the 2D data symbol, such asquadrature amplitude modulation (QAM), in R2, two IDHT devices 70 areused to perform multicarrier modulation in the transmitter. At thereceiver, the in-phase and quadrature-phase data path are fed into twoDHT processors 71 for demodulation. However, the data symbol on themirror-symmetric subcarriers will interfere with each other because ofthe inherent properties of DHT. Therefore this type of DHT-OFDM systemneeds multi-tap FEQ 73 to compensate the frequency-selective channelfading.

FIGS. 5 and 6 are the block diagrams of DHT-OFDM system in the priorarts, R1 and R2. A signal vector

in the receiver terminal can be expressed as

=H(Ã _(R) +jÃ ₁)H×

+

  (5)

(shown in FIG. 6) is an N×1 signal vector in the transmitter terminal, His an IDHT or DHT matrix, and

is a noise vector. When the length of CP is larger than the length ofmultipath channel delay, the channel effect can be expressed as acomplex circulant matrix Ã_(c)=Ã_(R)+jÃ₁. Equation (4) clearly showsthat the DHT cannot diagonalize the circulant channel matrix, thereforeequation (5) reveals that the receiver signal vector

will be interfered with the mirror-symmetric subcarriers; namely, thedata symbol d_(i) on the i-th subcarrier interferes the symbol d_(N−i)on the (N−i)-th subcarrier, i=1, . . . , N/2−1. That is the reason why,in the prior art R1, half of the signal bandwidth is waste to transmitthe repeated symbols for avoiding the inter-carrier interference causedby the channel effect. Besides, the other defect described in R1 is thefact that only the 1D modulation signal d_(i), such as a BPSK or PAMsignal, can be transmitted, which limits the bandwidth efficiency of thesystem. In the prior art R2, a multi-tap FEQ 73 is required tocompensate the inter-carrier interference caused by the channel effect,which makes the system complexity increase.

The main reason why the prior arts exist those defects is the DHT cannotdirectly diagonalize the equivalent circulant channel matrix, so themirror-symmetric subcarriers interfere with each other.

SUMMARY OF THE INVENTION

To solve the problem mentioned above, the present invention provides aDHT-based OFDM transmitter and receiver architecture based on discreteHartley transformation. The transmitter and receiver comprise two IDHT(or DHT) processors and one channel diagonalization processing device.The two IDHT processors make the DHT-OFDM system transmit the 2Dmodulation signal to increase the efficiency of bandwidth. Thediagonalization processing device is used to perfectly diagonalize theequivalent circulant channel matrix into discrete memorylesssubchannels, and thus only the simple one-tap FEQ is used to compensatethe channel. Besides, the DHT-OFDM transmitter and receiver are alsocompatible with the conventional DFT-OFDM one and can flexibly work withthe conventional DFT-OFDM transmitter and receiver.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a DHT-OFDM transmitter in an embodiment ofthis invention;

FIG. 2 is a block diagram of a DHT-OFDM receiver in an embodiment ofthis invention;

FIG. 3 is a block diagram of a combination of the DFT-OFDM transmitterand DHT-OFDM receiver in an embodiment of this invention;

FIG. 4 is a block diagram of a combination of the DHT-OFDM transmitterand DFT-OFDM receiver in an embodiment of this invention;

FIG. 5 is a block diagram of a conventional DHT-OFDM of 1D modulation;and

FIG. 6 is a block diagram of a conventional DHT-OFDM of 2D modulation.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, the present invention will be described more specifically withreference to the following embodiments. It is to be noted that thefollowing description of preferred embodiments of this invention ispresented herein for the purpose of illustration and description only;it is not intended to be exhaustive or to be limited to the precise formdisclosed.

With reference to FIGS. 1 through 4 a DHT-based OFDM transmitter andreceiver in this invention is illustrated. The OFDM transmitter is basedon the discrete Hartley transform architecture, as shown in FIG. 1, andcomprises a quadrature amplitude modulation (QAM) mapper 3, amulticarrier modulator, and a diagonal processing unit (DPU) 21. The QAMmapper 3 maps a bit stream to a 2D QAM signal vector

=

^(R)+j

¹. The DHT-based multicarrier modulator is connected to the QAM mapper3. The multicarrier modulator generates a OFDM modulation signal. Oneterminal of the DPU 21 is connected to the multicarrier modulator. TheDPU 21 comprises a component J_(N). The component J_(N) arranges asignal vector element in a retrograde order.

The multicarrier modulator comprises two inverse discrete Hartleytransform (IDHT) processors 10. The IDHT 10 modulate the 2D QAM signalvector

onto the N orthogonal subcarriers. Further, the diagonal processing unit(DPU) 21 is used to process IDHT output signal. Accompanying theproposed receiver design 30, the DPU can diagonalize the circulantchannel matrix to avoid the mirror-symmetric inter-carrier interference.The other terminal of the DPU 21 is further connected to a terminal of aP/S and CP adding unit 22. The P/S and CP adding unit 22 meansseries-to-parallel conversion, which converts a parallel vector signalbehind the DPU into a serial output. CP means Cyclic Prefix that isinserted before the serial output OFDM symbol. When the CP is inserted,the multipath channel matrix is equivalent to a circulant channelmatrix.

The other terminal of the P/S and add C/P unit 22 is connected to aterminal of a D/A converter 23. The D/A converter 23 means adigital-to-analog converter, which converts a discrete digital signalinto a continuous analog signal.

The other terminal of the D/A converter 23 is connected to a terminal ofa transmitter RF circuit 24, and the other terminal of the transmitterRF circuit 24 is further connected to a multipath fading channel 25. Thefunction of the transmitter RF circuit 24 is to modulate a basebandsignal to a high frequency signal. When the CP is inserted in the OFDMsystem and removed in the receiver, the multipath fading channel 25 canbe described as the circulant matrix.

Further, the OFDM receiver is based on the discrete Hartley transformarchitecture, as shown in FIG. 2, and comprises a multicarrierdemodulator 11, a DPU 34, a one-tap FEQ 35, and a QAM de-mapper 4. Themulticarrier demodulator is used to demodulate the OFDM signal. The DPU34 is connected to one terminal of the multicarrier demodulator.Accompanying the proposed DHT-based OFDM transmitter, the DPU 34 candiagonalize the circulant channel matrix. The one-tap FEQ 35 isconnected to the DPU 34. The one-tap FEQ 35 is used to compensate thechannel effects on each subcarriers. The QAM demapper 4 is connected tothe one-tap FEQ 35. The QAM demapper 4 maps the compensated QAM symbolto bit stream The one-tap FEQ 35 is comprised by a complex multiplier.The proposed DHT-OFDM system can diagonalize the circulant channelmatrix, so a complex multiplier is required on each subcarrier tocompensate the channel effects. The coefficients of FEQ can be expressedas equation (11).

The multicarrier modulator comprises two discrete Hartley transform(DHT) processors 11. The function of the DHT 11 is to demodulate the QAMsignal vector from the N orthogonal subcarriers. Along with the proposedtransmitter architecture 20, the DPU 34 can diagonalize the circulantchannel matrix to avoid the mirror-symmetric inter-carrier interference.

The other terminal of the multicarrier modulator is connected to aterminal of a S/P and CP removing unit 33. The S/P and CP removing unit33 removes the CP of OFDM signal, converts a serial data sequence into aparallel signal vector, and transmits the parallel signal vector to theDHT 11.

The other terminal of the S/P and CP removing unit 33 is connected to aterminal of an A/D converter 32. The A/D converter 32 means ananalog-to-digital (A/D) converter, and its function is to convert acontinuous analog signal into a discrete digital signal.

The other terminal of A/D converter 32 is connected to a terminal of areceiver RF circuit 31. The receiver RF circuit 31 demodulates thehigh-frequency signal down to a baseband signal.

The other terminal of the receiver RF circuit 31 is connected to anattenuation channel 25.

With reference to FIGS. 1 through 4, generally, the conventional OFDM isbased on discrete Fourier transform (DFT) for achievement ofmulticarrier modulation, and thus the system is named a DFT-based OFDMsystem. When CP is inserted before the OFDM symbol, and the length of CPis larger than the length of multipath channel delay spread, theDFT-OFDM system can diagonalize the equivalent circulant channel matrixinto the discrete memoryless subchannels. Thus, only one-tap FEQ caneasily compensate the channel, which is the reason why the DFT-basedOFDM system can mitigate the multipath channel fading. IFFT in FIG. 3 isan inverse fast Fourier transform; FFT in FIG. 4 is a fast Fouriertransform. Different from the complex-valued operation of DFT, the DHTbelongs to the transformation of real-valued operations, and thus theOFDM system based on DHT kernel has the advantages in computationalcomplexity and implementation. However, due to the inherent propertiesof DHT, DHT-OFDM cannot perfectly diagonalize the circulant channelmatrix as DFT-OFDM does even if the length of CP is larger than thelength of multipath channel delay spread. If the circulant channelmatrix cannot be diagonalized, the signals on the mirror-symmetricsubcarriers interfere with each other.

To sum up, the main problem of the prior art is the inability of theDHT-OFDM system to diagonalize the circulant channel matrix. In thisinvention, by using the inherence of DHT matrix, a simplediagonalization processor (i.e., DPU) is added to the DHT-OFDM system.With the DPU, the DHT-OFDM system can diagonalize the channel matrix.Thus, the receiver can compensate the channel effect by the one-tap FEQas the conventional DFT-OFDM does.

This invention relates to a DHT-OFDM system applicable to a 2Dmodulation. The DHT-OFDM system can diagonalize the circulant channeland also prevent the system mirror-symmetric subcarriers frominterfering with each other.

One objective of this invention is to design a DHT-OFDM system thatapplies to the 2D modulation, diagonalizes the circulant channel matrix,and also increases the efficiency of bandwidth to prevent thesubcarriers from interfering with each other. Another objective of thisinvention is to provide a DHT-OFDM transmitter or receiver that iscompatible with the conventional DFT-OFDM system; namely, the DHT-OFDMaccording to this invention can work with DFT-OFDM together.

For the purpose mentioned above, this invention uses two real-valuedIDHT/DHT transform processors in the DHT-OFDM transmitter or receiverfor achievement of 2D modulation. A diagonalization processor (i.e.,DPU) is added to the transmitter or receiver. The processor diagonalizesthe circulant channel matrix for the system.

The Improved DHT-OFDM System

The advancement of this invention is the improved DHT-OFDM system thattransmits the 2D modulation signal, such as QAM, and also diagonalizesthe circulant channel matrix. With this system, the multipath fadingchannel is diagonalized N discrete memoryless subchannels, which can beeasily compensated by one-tap FEQ. The detailed structure of thisinvention is described below.

FIG. 1 shows a block diagram of a DHT-OFDM transmitter system 20 in thisinvention; the function of the QAM mapper 3 is to map each bit stream toa 2D QAM signal vector

=

^(R)+j

¹. To modulate the 2D QAM to N orthogonal subcarriers by using the IDHT,the multicarrier modulator is expressed as per-envelop format H+jĤ,where Ĥ is the Hilbert transform of H. It can be expressed as:

$\begin{matrix}{\hat{H} = {{\frac{1}{\sqrt{N}}\left( {S - C} \right)} = {{{- J_{N}}H} = {- H^{\prime}}}}} & (6)\end{matrix}$

where H′=J_(N)H=HJ_(N). Thus, in FIG. 1, after the real and imaginaryparts of QAM signal fed into the IDHT multicarrier modulator in theper-envelop format, the in-phase and quadrature-phase sequences aregiven by:

$\begin{matrix}{{\;_{x}^{\rho_{R}}{+ j_{x}^{\rho_{I}}} = {{\left( {H + {j\hat{H}}} \right) \cdot \left( {\text{?} + \text{?}} \right)} = {\left( {\text{?} + \text{?}} \right) \cdot H \cdot \left( {\text{?} + \text{?}} \right)}}}{\text{?}\text{indicates text missing or illegible when filed}}} & (7)\end{matrix}$

The objective of proposed DHT-OFDM system is to diagonalize the channeleffect. In the reference [R3], it is inferred that there are two typesof matrices that can be diagonalized by DHT: one is symmetric circulantmatrix, and the other is J_(N) matrix multiplied by the skew-symmetriccirculant matrix. For this purpose, another DPU 34 is added before orafter the receiver DHT. Thus, the signal vector

in the receiver can be expressed as:

$\begin{matrix}\begin{matrix}{\mspace{79mu} {\text{?} = {{\text{?}\left( {\text{?} - \text{?}} \right){H \cdot \text{?}}} + \text{?}}}} \\{= {{\left( {D_{1} + {jD}_{2}} \right) \cdot \overset{\rho}{X}} + \overset{\rho}{W}}}\end{matrix} & (8) \\{\text{?}\text{indicates text missing or illegible when filed}} & \;\end{matrix}$

Let D=D₁+jD₂, then the equation (8) is expanded to obtain the matricesD₁ and D₂, as shown below.

$\begin{matrix}{\mspace{79mu} {{D_{1} = {{{H\text{?}H} + {{HJ}_{N}\text{?}H}} = {{2\left\{ \Lambda_{{\overset{\sim}{A}}_{R}} \right\}} - {2\left\{ \Lambda_{{\overset{\sim}{A}}_{I}} \right\}}}}}{\text{?}\text{indicates text missing or illegible when filed}}}} & (9)\end{matrix}$

D ₂ =H(Ã_(I) +J _(N) Ã ₁ J _(N))H+HJ _(N)(Ã _(R−J) _(N) Ã _(R) J_(N))H=2

{Λ_(Ã) _(I) }+2

{Λ_(Ã) _(R) }  (10)

From equations (9) and (10), it is apparent that the designed DPU1 andDPU2 in this invention can make the circulant channel matrix satisfywith the conditions of symmetry and skew-symmetric. In other words, theDHT-OFDM system can indeed make the channel matrix to be diagonalized.Thus, for one-tap FEQ 35, a zero-forcing (ZF) or minimum mean-squareerror (MMSE) coefficient as shown below can be used to compensate thechannel effects.

$\begin{matrix}\left\{ \begin{matrix}{E_{ZF} = D^{- 1}} \\{E_{MMSE} = {D^{H}\left( {{DD}^{H} + {\frac{\sigma_{w}^{2}}{\sigma_{x}^{2}}I_{N}}} \right)}}\end{matrix} \right. & (11)\end{matrix}$

Further, the DHT-OFDM transmitter or receiver in this invention hasanother advantage of compatibility with a general DFT-OFDM transmitteror receiver. As shown in FIG. 3, the signal from the DFT-OFDMtransmitter can be demodulated directly by the proposed DHT-OFDMreceiver in this invention and does not need additional signalprocessing. It is because the circulant channel matrix can bediagonalized by the hybrid DFT-OFDM transmitter and DHT-OFDM receiver.To verify the channel diagonalized fact, the signal vector

′ in the receiver shown in FIG. 3 can be expressed as:

$\begin{matrix}{\mspace{85mu}_{Y}^{\rho_{\prime \; R}}{{{+ j_{Y}^{\rho_{\prime \; I}}} = {{\left( {\text{?} + \text{?}} \right)H{\overset{\sim}{A}}_{C}{F \cdot \overset{\rho}{X}}} + \overset{\rho}{W}}}{\text{?}\text{indicates text missing or illegible when filed}}}} & (12)\end{matrix}$

Deriving equation (12) by the DHT properties, it can be show in equation(13) that the matrix D′ is a diagonal matrix:

D′=(

{Λ _(Ã) _(R) −ℑ{Λ_(Ã) _(R)}−ℑ{Λ_(Ã) _(I)}−

{Λ_(Ã) _(I) })+j(

Λ_(Ã) _(R) }+ℑ{Λ_(Ã) _(R) }+

{Λ_(Ã) _(I) }−ℑ{Λ_(Ã) _(I) })  (13)

Similarly, in FIG. 4, the DHT-OFDM transmitter signal can also bedemodulated by the DFT-OFDM receiver. The signal vector

″ at the receiver in FIG. 4 can be expressed as:

$\begin{matrix}{\mspace{79mu} {{{\overset{\rho}{Y}}^{\prime\prime} = {{\text{?} \cdot \overset{\rho}{X}} + \overset{\rho}{W}}}{\text{?}\text{indicates text missing or illegible when filed}}}} & (14)\end{matrix}$

where matrix D″ is also a diagonal matrix as follows:

D″=(

{Λ_(AÃ) _(R)}+ℑ{Λ_(Ã) _(R)}−ℑ{Λ_(Ã) _(I) }+

{ΛÃ_(I)})+j(−

{Λ_(Ã) _(R) }+ℑ{ΛÃ _(R) }+

{Λ_(Ã) _(I) }+ℑ{Λ_(Ã) _(I) })  (15)

From equation (13) and (15), it is apparent that the multipath channelmatrix can be diagonalized when the proposed DHT-OFDM transceiver workswith the conventional DFT-OFDM transceiver; namely, only the simpleone-tap FEQ is required to compensate the channel effects. Therefore,this invention not only is available for the mentioned DHT-OFDM system,but also flexibly and easily works with the conventional DFT-OFDMtransmitter.

To sum up, the main function of this invention is to increase theefficiency of bandwidth and prevent the subcarriers from interferingwith each other. Further, the DHT-OFDM transmitter or receiver in thisinvention is compatible with the conventional DFT-OFDM; namely, theDHT-OFDM system in this invention works with the DFT-OFDM system.

While the invention has been described in terms of what is presentlyconsidered to be the most practical and preferred embodiments, it is tobe understood that the invention needs not be limited to the disclosedembodiment. On the contrary, it is intended to cover variousmodifications and similar arrangements included within the spirit andscope of the appended claims which are to be accorded with the broadestinterpretation so as to encompass all such modifications and similarstructures.

REFERENCE

-   [R1] D. Wang, D. Liu, F. Liu, and G. Yue, “A novel DHT-based    ultra-wideband system,” in Proc. ISCIT, October, 2005, vol. 1, pp.    672-675.-   [R2] R. Merched, “On OFDM and single-carrier frequency-domain    systems based on trigonometric transforms,” IEEE Trans. Signal    Process., vol. 13, no. 8, pp. 473-476, August 2006.-   [R3] G. Heinig and K. Rost, “Representation of Toeplitz-plus-Hankel    matrices using trigonometric transformations with application to    fast matrix-vector multiplication,” Linear Algebra Appl., vol.    275-276, pp. 225-248, 1998.

1. A DHT-based OFDM transmitter, comprising: a quadrature amplitudemodulation (QAM) mapper, mapping a bit stream to a 2D QAM signal vector

=

^(R)+j

^(I); a multicarrier modulator, being connected to the QAM mapper andgenerating an OFDM modulation signal with multiple carriers; and adiagonalization processing unit (DPU), wherein a terminal is connectedto the multicarrier modulator, the DPU comprising a component J_(N), inwhich the component J_(N) arranges a signal vector element in aretrograde order, and the DPU processes a modulated signal after themulticarrier modulator to make a circulant channel matrix bediagonalized.
 2. The DHT-based OFDM transmitter according to claim 1,wherein the multicarrier modulator comprises two inverse discreteHartley transform (IDHT) processors, and the IDHT modulates the 2D QAMsignal

onto the N orthogonal subcarriers.
 3. The DHT-based OFDM transmitteraccording to claim 1, wherein the other terminal of the DPU is connectedto a terminal of a P/S and CP adding unit.
 4. The DHT-based OFDMtransmitter according to claim 3, wherein the other terminal of the P/Sand CP adding unit is connected to a terminal of a D/A converter.
 5. TheDHT-based OFDM transmitter according to claim 4, wherein the otherterminal of the D/A converter is connected to a terminal of atransmitter RF circuit and the other terminal of the transmitter RFcircuit is further connected to a multipath fading channel.
 6. ADHT-based OFDM receiver, comprising a multicarrier demodulator, beingused to demodulate the OFDM signal; a diagonalization processing unit(DPU), being connected to the multicarrier demodulator and being used tomake a DHT-OFDM receiver diagonalize a circulant channel matrix; aone-tap frequency-domain equalizer, being connected to the DPU and beingused to compensate channel effect on each subcarriers; and a quadratureamplitude modulation (QAM) de-mapper, being connected to the one-tapfrequency-domain equalizer and mapping a compensated QAM symbol to a bitstream.
 7. The DHT-based OFDM receiver according to claim 6, wherein themulticarrier demodulator comprises two discrete Hartley transform (DHT)processors.
 8. The DHT-based OFDM transmitter according to claim 7,wherein one terminal of the multicarrier modulator is further connectedto a terminal of an S/P and a CP removing unit.
 9. The DHT-based OFDMtransmitter according to claim 8, wherein the other terminal of the P/Sand CP removing unit is connected to a terminal of a D/A converter. 10.The DHT-based OFDM transmitter according to claim 9, wherein the otherterminal of the A/D converter is connected to a terminal of a receiverRF circuit.
 11. The DHT-based OFDM transmitter according to claim 10,wherein the other terminal of the receiver RF circuit is connected to amultipath fading channel.